In the aged society, it has become more important than in the past to develop technologies for human assist. In this paper, a power assist system for the attendant of an omni-directional transport wheelchair is developed. The applied force of the attendant is measured by a force sensor attached to handles of the wheelchair. The desired motion of the wheelchair is estimated from the output signal of the force sensor using fuzzy reasoning. Then, it is transmitted to four motors of the wheelchair to make it move toward desired direction. The effectiveness of the proposed method is examined by experiments.